In the semiconductor industry, there is a continuing trend toward more complex feature shapes. To achieve these more complex feature shapes there have been, and continue to be, efforts directed at creating more precise features, with more precise critical dimensions and angles. In order to reproduce such complex devices from wafer to wafer and within a wafer, finer control of lithographic processes (e.g., etch processes) is required to mitigate structural variations from feature to feature.
The requirement of small, complex features with close spacing between adjacent features requires sophisticated manufacturing techniques, including high-resolution photolithographic processes, and controlling post development etch trim processes. Fabricating a semiconductor using such sophisticated lithography techniques may involve a series of steps including cleaning, thermal oxidation or deposition, masking, developing, etching, baking and doping.
In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the photoresist. The photoresist coated substrate is baked to evaporate any solvent in the photoresist composition and to fix the photoresist coating onto the substrate. The baked coated surface of the substrate is next subjected to selective radiation using a mask; that is, a mask is employed to effect an image-wise exposure to radiation. The mask permits radiation to contact certain areas of the photoresist and prevents radiation from contacting other areas of the photoresist. This selective radiation exposure causes a chemical transformation in the exposed areas of the photoresist coated surface. Types of radiation commonly used in microlithographic processes include visible light, ultraviolet (UV) light and electron beam radiant energy. After selective exposure, the photoresist coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist (depending upon whether a positive photoresist or a negative photoresist is utilized) resulting in a patterned or developed photoresist.
The process of manufacturing semiconductors, or integrated circuits (commonly called ICs, or chips), typically consists of more than a hundred steps, during which hundreds of copies of an integrated circuit may be formed on a single wafer. Each integrated circuit may have a large number (e.g., millions) of features with a variety of shapes. Generally, the process involves creating several patterned layers on and into the substrate that ultimately forms a complete integrated circuit. This layering process creates electrically active regions in and on the semiconductor wafer surface. The accuracy of the reproduction of the shapes of multi-sloped features are important to the proper separation and operation of such electrically active regions. Conventional systems suffer from not being able to adapt processes to the individual characteristics associated with the multi-sloped features on a wafer and thus yields may be lower than are possible if more sophisticated monitoring and adapting techniques were employed.
Due to the extremely fine patterns associated with complex multi-sloped features that are exposed on the photoresist, controlling the multi-slope profile etch process is a significant factor in achieving and reproducing desired critical dimensions. Regulating the etching process in-situ may facilitate obtaining more precise, more complex multi-sloped feature profiles and thus increase the quality of the complicated devices being manufactured on the wafer. Even slight changes in etch process conditions can substantially alter the etch accuracy of the multi-sloped feature profiles, resulting in poor feature formation and IC performance. Conventional systems may not be able to account for such slight changes, and thus less precise features may be etched. Thus, there remains a need for a more precise system for monitoring the formation of multi-sloped features.